This project will continue our long term interest in investigating the mechanisms of control of lung cancer cell behavior, focusing on ras/raf-mediated signal transduction pathways. We have shown that raf activation can induce growth arrest in small cell lung cancer (SCLC), but not in non small cell lung cancer (NSCLC), This growth arrest is accompanied by induction of cyclin dependent kinase inhibitor expression; in at least some cell lines, p27Kip1 is induced by translational control. We hypothesize!) that raf activation may mediate growth arrest via translational control in SCLC cells, 2) that this growth arrest can be blocked by activation of rho family protein signal transduction, which may be more active in NSCLC than in SCLC cells, and 3) raf effects on SCLC cells may be mediated in part by autocrine or paracrine mechanisms. The level of activation of the rho family signal transduction pathway will be examined in SCLC and NSCLC cells. In a complementary series of studies, the effect of activating or inhibiting rho family signal transduction in SCLC cells will be investigated, focusing on the effects of rho family members on raf-mediated growth arrest. The mechanism of induction of p27kip1 by translational activation during raf-mediated growth arrest in SCLC cells will be investigated. The role of the translation initiation factor eIF4E will be examined. The ability of translational activation to induce cyclin dependent kinase inhibitors and cell cycle arrest in SCLC cells will be determined. The role of autocrine ligands in mediating the effects of raf activation in SCLC cells will be investigated. Identification of two raf-induced autocrine lung cancer derived factors, LCDF I and LCDF2, will be completed. LCDF 1 induces Phosphorylation of MAPK and accumulation of p27, and LCDF2 induces morphological changes in SCLC cells. The ability of LCDF I to promote growth arrest will be determined. The receptor for LCDF 1 will be isolated, and its signal transduction pathways will be identified. The expression patterns for LCDF 1 and its receptor, and LCDF2, will be determined in lung cancer cell lines and primary tumors. The factors responsible for raf-mediated induction of LCDF 1 in SCLC cells will be identified.